Depending on your machine you can try piping your strings through
iconv -f utf-8 -t ascii//translit
(or whatever your encoding is, if it's not utf-8)
You might be able to use iconv.
For example, the string:
Žvaigždės aukštybėj užges or äüöÖÜÄ
is in file testutf8.txt, utf8 format.
Running command:
iconv -f UTF8 -t US-ASCII//TRANSLIT testutf8.txt
results in:
Zvaigzdes aukstybej uzges or auoOUA
echo Hej på dig, du den dära | iconv -f utf-8 -t us-ascii//TRANSLIT
gives:
Hej pa dig, du den dara